Photoelectronic signal generation in scanning television optical microscope

V. Goy, B. Hudz, V. Shkliarskyi

Lviv Polytechnic National University

This paper presents a method of determining the necessary sensitivity for photoelectronic transducer (PET) in scanning television optical microscope (STOM), which is used for biological microobject studying. High resolution cathode ray tube is used in the STOM for test microobject illumination. On the screen of this tube a scanning raster is being formed. This raster allows you to create an image of microobjects, whose resolution exceeds 4000x4000 elements. The proposed principle of microobject scanning using light probe with subsequent computer image processing has several advantages compared to optical microscopy – possibility of quantitative measurements within individual fragments of tested microobjects; flexibility to control the measurement process; reducing the duration of the study; higher resolution. These advantages allow to use the new method for studying microobjects extensively, including the ultraviolet radiation range.
To generate an electric signal which amplitude is proportional to the luminous flux coming from the test microscopic element, PET is being used. The method for determining sensitivity of the PET is proposed in this article. This technique takes into account the design parameters of optical channel: transmission ratio of condenser lens in the optical channel; the solid angle within which the luminous flux from the object reaches the condenser lens, the entrance pupil area of condenser lens. While determining the required PET sensitivity load impedance of transducer, required signal/noise ratio for obtaining desired quality of the formed image and video bandwidth for the selected definition of microscopic images are considered.
The classification of PET, suitable for use in the STOM, which will optimize the choice of the PET for the optical channel, depending on the capabilities of the microscope and its alleged main technical parameters is developed. The main classification PET features are: physical operation principle, spectral operation range, number of photosensitive elements, number of optical data input channels, frequency properties, and type of output signal.
Technical parameters of test microobjects, which are required to be guaranteed in the STOM when the microobject is in the ultraviolet range are described. The spectral response of the photocathode was used as the first selection criteria for ultraviolet spectrum usage. From constructional point of view, it is desirable to have a uniform sensitivity transducer over the entire range of the radiation from 250 nm to 700 nm. Analysis of transducers distributed on the territory of the CIS countries, has shown that there is no transducer that would overlap the above-mentioned range with sufficient uniformity of sensitivity. Therefore, PET analysis was focused on choosing those of them which overlaps certain spectrum bands at maximum sensitivity.